Techniques for dual modulation with light conversion

ABSTRACT

Techniques for driving a dual modulation display include generating backlight drive signals to drive individually-controllable illumination sources. The illumination sources emit first light onto a light conversion layer. The light conversion layer converts the first light, such as blue or ultraviolet light, into second light, such as white light. The light conversion layer can include quantum dot materials. Liquid crystal display (LCD) modulation drive signals are generated to determine transmission of the second light through individual color subpixels of the display. These LCD modulation drive signals can be adjusted based on one or more light field simulations to account for non-uniform, spatial color shifts. Alternatively, one or more light field simulations based on a uniformity assumption determine intermediate LCD modulation drive signals. A compensation field simulation, using backlight drive signals, is then used to adjust the intermediate LCD modulation drive signal for color correction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to United StatesProvisional Patent Application No. 62/040,352 filed 21 Aug. 2014, whichis hereby incorporated by reference in its entirety.

TECHNOLOGY

The present invention relates generally to display techniques, and inparticular, to display techniques for dual modulation with lightconversion.

BACKGROUND

Color filter arrays in liquid crystal displays (LCDs) and organiclight-emitting diode (OLED) displays are commonly produced byphotolithographic techniques, or printing techniques, as part of the LCDand OLED panel production process. Color filters in emissive displayssuch as LCD and OLED displays typically consist of red, green and bluefilters. The color filters are patterned over the pixel array to allowthe pixel elements to modulate the emitted light by color, as well as byintensity. In operation, a broadband light source (e.g., white light)provides light to pixel elements, for example, in LCD display systems.Alternatively, broadband light is created by white OLED pixel elementsin OLED display systems. A pixel element can vary the intensity of thebroadband light transmitting out of the pixel element. The intensitymodulated broadband light of each pixel element can be further colorfiltered by overlaying color filters. Considerable light is wasted bycolor filters because, for example, in order to produce red lightspectrum (e.g., about 620-740 nanometers), then green light (e.g., about520-570 nanometers) spectrum and blue light spectrum (e.g., about450-495 nanometers) of the broadband light source would be blocked.Additionally, this wasted light is converted into harmful heat whichdegrades the performance and lifetime of the display system.

Thus, engineering a display system with wide color gamut and highluminance has been recognized as a costly endeavor by many displaymanufactures. Because of a high number of relatively expensive optical,audio, electronic and mechanical components involved and the complexityin integrating all of them into a single system, the cost ofmanufacturing a praiseworthy display system is typically very high.

Accordingly, it is seen by the inventors here that a dual modulationdisplay with light conversion can provide many performance benefits overconventional techniques employing color filters. Additionally, asdiscovered by the inventors, introduction of light conversion to a localdimming display architecture results in color non-uniformity color.Techniques to compensate for color non-uniformity, particularly for awhite light local dimming display, are provided.

The approaches described in this section are approaches that could bepursued, but not necessarily approaches that have been previouslyconceived or pursued. Therefore, unless otherwise indicated, it shouldnot be assumed that any of the approaches described in this sectionqualify as prior art merely by virtue of their inclusion in thissection. Similarly, issues identified with respect to one or moreapproaches should not assume to have been recognized in any prior art onthe basis of this section, unless otherwise indicated.

SUMMARY OF THE DESCRIPTION

Methods and apparatuses for driving a dual modulation display (alsoreferred to herein as a local dimming display) are provided.Illumination sources emit first light onto a light conversion layer. Thelight conversion layer converts the first light into second light.Modulation drive signals to determine transmission of the second lightcan be adjusted based, in part, on one or more light field simulations.

As an embodiment of the present invention, driving a local dimmingdisplay includes generating backlight drive signals to driveindividually controllable illumination sources. The illumination sourcesemit first light onto a light conversion layer. The light conversionlayer converts the first light into second light. The light conversionlayer can include quantum dots (QD) or phosphor materials. Modulationdrive signals are generated to determine transmission of the secondlight through individual subpixels of the display. These modulationdrive signals can be adjusted based on one or more light fieldsimulations. The light field simulations can address: (i) a resultingcolor shift for a pixel based on a point spread function of theillumination sources; (ii) binning difference of individual illuminationsources; (iii) temperature dependence of display components onperformance; or (iv) combinations thereof.

As another embodiment of the present invention, a method for driving alocal dimming display includes generating, based on image data,backlight drive signals to drive individually controllable, lightemitting diode (LED) sources of a backlight. The individuallycontrollable LED sources emit a first light onto a quantum dot layer,which converts at least a portion of the first light (as well as,optionally, recycled light within the display) into second light. LCDmodulation drive signals, regulating transmission of the second lightthrough individual subpixels of the display by an LCD array, aredetermined. An increase in yellow light spectral components for a pixelbased upon one or more of the backlight drive signals and respectivedistances between the pixel and one or more LED sources is determined.The LCD modulation drive signal for at least one subpixel of the pixelis adjusted to reduce yellow light spectral components when renderingthe pixel.

As yet another embodiment of the present invention, a display systemincludes one or more illumination sources of a backlight configured toemit first light. The first light can include ultraviolet (UV) spectralcomponents (e.g., about 10-400 nanometers) and/or blue light spectralcomponents. The display further includes one or more light conversionlayers configured to be stimulated by the first light and to convert atleast a portion of the first light into second light. Light modulatorsare configured to modulate an amount of second light transmitted throughindividual subpixels of the display system. Logic computes one or morelight field simulations for (i) color shifts as a function of abacklight point spread function, (ii) a difference between a performancecharacteristic of an illumination source of the one or more illuminationsources of the backlight and a performance characteristic of thebacklight, (iii) temperature variance for a rendered pixel, orcombinations thereof. A controller can adjust drive values for the oneor more light modulators based on the light field simulation.

As another embodiment of the present invention, driving a dualmodulation display includes generating backlight drive signals forindividually-controllable illumination sources. The illumination sourcesemit first light, such as ultraviolet or blue light, onto a lightconversion layer. The light conversion layer converts the first lightinto second light, such as white light. The light conversion layer caninclude quantum dot materials. Intermediate liquid crystal display (LCD)modulation drive signals are determined based on one or more light fieldsimulations, which assumes little or no spatial color shift. Theseintermediate LCD modulation drive signals can be adjusted based on oneor more color field simulations to account for non-uniform, spatialcolor shifts resulting from using the light conversion layer.

BRIEF DESCRIPTION OF DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 illustrates an exemplary color array panel comprising aconversion layer;

FIGS. 2A, 2B and 2C illustrate an example PSF having a color shift as afunction of distance from center.

FIG. 2D illustrates an example PSF having a spatially varying colorshift for backlight of blue LEDs.

FIG. 3 illustrates an exemplary configuration of display logic in adisplay system;

FIG. 4 illustrates an exemplary flow diagram for driving a local dimmingdisplay; and

FIG. 5 illustrates an example hardware platform on which a computer or acomputing device as described herein may be implemented, according apossible embodiment of the present invention.

FIGS. 6A and 6B illustrate simplified configurations of local dimmingwith light conversion.

DESCRIPTION OF EXAMPLE POSSIBLE EMBODIMENTS

The following description and drawings are illustrative of the inventionand are not to be construed as limiting the invention. Numerous specificdetails are described to provide a thorough understanding of theinvention. However, in certain instances, well known or conventionaldetails are not described in order to avoid obscuring the description ofthe invention. Additionally, details from U.S. patent application Ser.No. 14/370,115, entitled “Techniques for Dual Modulation Display withLight Conversion,” is hereby incorporated by reference for all purposes.

FIG. 1 illustrates an exemplary color array panel 100 comprising anoptical stack 101. Optical stack 101 can include, without limitation:

i. conversion layer 102;

ii. illumination sources 104;

iii. reflector surface 106;

iv. diffuser layer 108;

v. light recycling film 110; and

vi. light modulation layer 112.

Conversion layer 102, disposed in front (from a viewer's perspective) ofillumination sources 104, can comprise quantum dot or phosphormaterials. Quantum dot (e.g., nano-scale particles using a quantumconfinement effect for light emission) or phosphor materials can becoated, attached to, doped, or otherwise disposed on a top surface,bottom surface, or both surfaces of an optical layer to form conversionlayer 102. Quantum dot or phosphor materials may also be embedded withinthe optical layer. These materials may be disposed with the opticallayer in any combination or order of various disposition methods.

Conversion layer 102, using quantum dot color arrays or phosphor colorarrays, impart colors in a color display system. A red quantum dot orphosphor material absorbs light of higher energies or shorterwavelengths such as green and blue light and emits red light. A greenquantum dot or phosphor material absorbs blue light and emit greenlight. Accordingly, as an embodiment of the present invention,conversion layer 102 produces desired colors: red and green lightconverted from a blue light source; while blue light is emitted from theblue light source directly.

In an embodiment of the present invention, conversion layer 102 is asingle sheet (or, alternatively, multiple of segments arranged to form asingle plane) extending, in width and height, to be substantially equalto dimensions of an active area of the display device. For example,conversion layer 102 can measure, diagonally, about 4 inches, 10 inches,32 inches, 40 inches, 50 inches, 58 inches or more. Additionally,conversion layer 102 can have an aspect ratio, or the proportionalrelationship between width and height, of 16:9, 4:3, 3:2, 5:3, 5:4, or1:1, among others. As illustrated in FIG. 1, conversion layer 102 isdisposed away from illumination source 104. In an alternative embodimentof the present invention, conversion layer 102 comprises a plurality ofsegments. In a specific embodiment, each segment of the plurality ofsegments is associated with a single illumination source 104.

Illumination sources 104 can be any source of electromagnetic energyuseable by conversion layer 102 to produce perceptible light for humanor machine vision. For example, illumination sources 104 can include oneor more of OLED, RGB LED, broadband LED, blue spectrum LED, ultravioletspectrum LED, or the like.

These illumination sources 104 can be arranged as an array extendingsubstantially the length and height of the active area of the displaydevice. The pitch density between illumination sources 104 can equal orcorrespond to the pixel resolution of the display. That is to say, theratio of illumination sources 104 to the number of pixel can be 1:1(e.g., 1920×1080, 3840×2160, or 7680×4320 illumination sources forrespective display resolution). In this case, the position of each ofthe illumination sources 104 can be directly aligned behind (fromviewer's perspective) a corresponding pixel. In other cases,illuminations sources 104 can be disposed with a lateral offset from acorresponding pixel or between two pixels. The pitch betweenilluminations sources 104 can be uniform or non-uniform, for example,pitch density can be higher in proximity to a central active area ofdisplay than in a periphery, edges, corners, or black borders inletterbox format.

In other embodiments, the ratio between of illumination sources 104 tothe number of pixel can be lower, such as 1:2, 1:3, 1:4, 1:10, or more.In this case, the resolution of the backlight image will be decreased.Alternatively, the ratio can be higher, such as 2:1, 3:1, or less. Forexample, an illumination source can be associated with a subpixel,instead of a pixel or group of pixels.

These illumination sources 104 are individually controlled or,alternatively, a subset of them can be collectively controlled inunison. The flexibility of backlight control through individuallycontrollable illumination sources 104 permits local dimming. Additionaldetails about local dimming can be found in U.S. Pat. No. 8,277,056,entitled “Locally Dimmed Display,” which is hereby incorporated byreference in its entirety for all purposes. However, despite individualcontrol of illumination sources 104, the PSF for each of illuminationsources 104 can overlap to contribute to the intensity of a plurality ofpixels.

Although FIG. 1 illustrates a direct-lit backlight display, an edge-litdisplay can also enjoy the benefits of the inventions taught in thisdisclosure (e.g., compensation for color shift from PSF, illuminationsource binning, or temperature variance). In such an embodiment, aspatial light modulator illuminated by one or more light sourcespositioned at an edge of the spatial light modulator. Additional detailsabout edge-lit, local dimming can be found in U.S. Pat. No. 8,172,401,entitled “Edge Lit Locally Dimmed Display,” which is hereby incorporatedby reference in its entirety for all purposes.

Reflector surface 106 can be a broadband mirror surface, dichroic mirrorsurface reflecting a predetermined spectrum (e.g., one or more primarycolors). Further, reflector surface 106 can include through-holes forillumination sources 104. These through-holes can be reamed, drilled, ormilled. Reflector surface 106 redirects light back through the opticalstack 101 for increased efficiency.

In FIG. 1, diffuser layer 108 scatters outgoing light through a range ofdirections so that a viewer located on an opposite side of diffuser 108perceives light to originate from an increased area. In general,diffuser 108 can scatter light to a different angular extent in thehorizontal and vertical planes.

Light recycling film 110 is used to boost the optical efficiency ofbacklighting. In some embodiments, as light modulation layer 112 canonly (or substantially only) pass polarized light and that the backlightessentially produces unpolarized light. A reflective polarizer (e.g., 3MDBEF) can be used as the last optical layer before light modulationlayer 112. Light of the wrong polarization incident on the lightmodulation layer 112, which would otherwise be absorbed, is reflectedback by the light recycling film 110 towards the backlight. Thereflected light would be scattered in diffuser layer 108 whichrandomizes the polarization. The reflected light having randomizedpolarization, which has a fraction of the correct polarization to passthrough the light modulation layer 112, can be redirected toward thelight modulation layer 112 as it scatters and bounces in the opticalstack.

Another light recycling film 110 can be a prismatic structured film(e.g., 3M BEF) which is used to control the direction of light exitingthe backlight unit. To maximize the intensity of light within theviewing angle of light modulation layer 112, light outside of theviewing angle can be reflected back into the optical cavity which afterscattering and reflection can result in a fraction of the reflectedlight having the desired exiting angle within viewing angle.

Light modulation layer 112 may comprise, for example, (i) an LCD panel,which is an example of a transmission-type light modulator, (ii) adeformable mirror device (DMD), which is an example of a reflection-typelight modulator, or (iii) a micro-electro-mechanical system (MEMS) basedmodulator. The elements of light modulator 112 are controlled accordingto data which defines an image being displayed.

It should be appreciated that FIG. 1 illustrates an embodiment ofoptical stack 101, and the arrangement of elements therein can vary orcan include additional elements not described. For example, lightrecycling film 110 can be disposed behind diffuser layer 108, ratherthan in front of it. As yet another example, conversion layer 102 can bedisposed anywhere within optical stack 101 after illumination sources104. All such modifications and variations are intended to be includedwithin the scope of this disclosure.

As appreciated by the inventors here, exemplary color array panel 100suffers from a “yellow tail effect,” or a point spread function (PSF)that shifts colors as a function of distance from center. That is tosay, light traveling a relatively long optical path, redirected back tospatial regions close to or in light sources, can be spatially spreadinto wide angles and areas, and cause color shifts (e.g., yellowtails)—particularly with light recycling with one or more reflections.In such a system, for example, the light in the center of a point spreadfunction of a direct-lit light emitter would be mostly converted, butrejected light components can bounce back in and convert with less greenand red as the distance from the center of the point spread function ofthe light emitter to outer circumferences increases, giving rise to acolor shift to the point spread function (PSF). The PSF tail becomesincreasingly yellow even when the PSF center has a desired white point.Without the presence of compensation, color shift degradation may beespecially noticeable or even visually prominent. FIGS. 2A, 2B and 2C,as simple illustrations, show the yellow tail effect. FIG. 2Dillustrates an example PSF having a spatially varying color shift forbacklight of blue LEDs.

FIG. 3 illustrates an exemplary configuration of display logic in adisplay system 300. In accordance with some possible embodiments of thepresent invention, display system 300 includes backlight control logic302 to control illumination sources in backlight 304. These illuminationsources may be same or similar to illumination sources 104 shown inFIG. 1. Backlight control logic 302 can be operatively coupled with animage data source (not shown) (e.g., a set-top box, networked server,storage media or the like) and is configured to receive image data fromthe image data source. Image frames received or generated from imagedata from an internal or external source may be used by the backlightcontrol logic 302 to drive the backlight 304. For example, backlightcontrol logic 302 may be configured to control backlight 304 toilluminate one or more pixels or sub-pixels with a specific intensity.The image frames may be used by the backlight control logic 302 toderive individual or aggregate drive values in various frames in variousresolutions.

In this embodiment of the present invention, backlight control logic 302is logically coupled to light field simulation logic 306. Light fieldsimulation logic 306 computes one or more influences on the light field,such as, for example, the yellow tail effect, illumination sourcebinning, temperature dependence on system components and the like. Basedon these influences, light field simulation logic 306 and/or modulatorcontrol logic 308 (e.g., LCD panel control logic) can mitigate them forimproved picture quality. For example, to mitigate the yellow taileffect, drive values to the modulator 310 (e.g., an LCD panel) can bebiased to be more blue.

In one embodiment, a light field simulation can utilize nine convolutionchannels representing three color tristimulus values for each of thethree primary colors. However, this is computationally expensive. As analternative, the light field simulation can model the individuallycontrollable illumination sources of the backlight as having a first PSFfor broadband light spectral components and a second PSF for yellowlight spectral components—or two convolution channels, not nine. Thefirst PSF is narrower than the overlapping second PSF from the yellowtail effect.

Light field simulation logic 306 can include a convolution channel tocompensate for binning (lack or insufficiency thereof) of backlight LEDs(e.g., illumination sources 102). For a broadband backlight, white LEDs,constructed with blue LED dies and yellow phosphor (e.g., YAG phosphor),can be used. However, binning variation of white LEDs with wideperformance ranges can reduce display accuracy and uniformity. Inparticular, the yellow phosphor material on each blue LED die can varycausing a differing white point. The yellow phosphor on each blue LEDdie can also have varying spectral emission. Similarly, in an embodimentexclusively using UV and/or blue spectral components for backlighting,these UV or blue LEDs can have different intensity for constant power orvary in emission spectrums.

As embodiment of the present invention, light field simulation logic 306can be used to compensate for temperature dependence of displayperformance with additional convolution channels. For example, deratingfunction(s) can be used to account, either individually or collectively,for temperature dependence of illumination sources or a conversionlayer. As another example, a temperature dependent point spread functioncan be used to address optical sheet warping. In a specific embodiment,one or more temperature measurements can be taken from one or moresensors (disposed within the optical stack) or temperature can beinferred by a display characteristic (e.g., performance change overtime).

FIG. 4 illustrates an exemplary flow diagram 400 for driving a localdimming display. In step 402, drive signals for the backlight (e.g.,illumination sources 104) can be generated. The driven backlightproduces a first light, in step 404. The first light can be a broadbandlight (e.g., white light), UV spectral components, blue spectralcomponents, or any portion of the spectrum. As shown in step 406, firstlight is converted into a second light. For example, a conversion layerreceives the first light produces second light with desired colors(e.g., red or green light).

Next, in step 408, drive values for a modulator (e.g., an LCD panel),preferably a subpixel modulator for each primary color, are generatedbased on input image data. The results of the one or more light fieldsimulations can be used to adjust, modify or weigh modulator drivevalues, as reflected in step 412. One or more light field simulationsfor compensation are performed in step 410. As described herein, lightfield simulations can address, as examples, (i) color shifts as afunction of a backlight point spread function, (ii) a difference betweena performance characteristic of an illumination source of the one ormore illumination sources of the backlight and a performancecharacteristic of the backlight, (iii) temperature variance onperformance, or (iv) combinations thereof.

It is appreciated that flow diagram 400 described herein is forillustrative purposes only and that various modifications or changes inlight thereof will be suggested to persons skilled in the art. Inalternative implementations, the steps noted in flow diagram 400 mayoccur out of the order noted in FIG. 4, may include additional steps,and/or may omit some steps altogether. For example, steps 402 and 408may in fact be executed substantially concurrently or in reverse order.As another example, step 410 can be performed before step 404. All suchmodifications and variations are intended to be included within thescope of this disclosure.

Embodiments include an apparatus comprising a processor and configuredto perform any one of the foregoing methods as discussed above.

Embodiments include a computer readable storage medium, comprisingsoftware instructions, which when executed by one or more processorscauses performance of any one of the foregoing methods as discussedabove.

Implementation Mechanisms—Hardware Overview

According to one embodiment, the techniques described herein areimplemented by one or more special-purpose computing devices. Thespecial-purpose computing devices may be hard-wired to perform thetechniques, or may include digital electronic devices such as one ormore application-specific integrated circuits (ASICs) or fieldprogrammable gate arrays (FPGAs) that are persistently programmed toperform the techniques, or may include one or more general purposehardware processors programmed to perform the techniques pursuant toprogram instructions in firmware, memory, other storage, or acombination. Such special-purpose computing devices may also combinecustom hard-wired logic, ASICs, or FPGAs with custom programming toaccomplish the techniques. The special-purpose computing devices may bedesktop computer systems, portable computer systems, handheld devices,networking devices or any other device that incorporates hard-wiredand/or program logic to implement the techniques.

For example, FIG. 5 is a block diagram that illustrates a computersystem 500 upon which an embodiment of the invention may be implemented.Computer system 500 includes a bus 502 or other communication mechanismfor communicating information, and a hardware processor 504 coupled withbus 502 for processing information. Hardware processor 504 may be, forexample, a general purpose microprocessor.

Computer system 500 also includes a main memory 506, such as a randomaccess memory (RAM) or other dynamic storage device, coupled to bus 502for storing information and instructions to be executed by processor504. Main memory 506 also may be used for storing temporary variables orother intermediate information during execution of instructions to beexecuted by processor 504. Such instructions, when stored in storagemedia accessible to processor 504, render computer system 500 into aspecial-purpose machine that is customized to perform the operationsspecified in the instructions.

Computer system 500 further includes a read only memory (ROM) 508 orother static storage device coupled to bus 502 for storing staticinformation and instructions for processor 504. A storage device 510,such as a magnetic disk or optical disk, is provided and coupled to bus502 for storing information and instructions.

Computer system 500 may be coupled via bus 502 to a display 512, such asa liquid crystal display (LCD), for displaying information to a computeruser. An input device 514, including alphanumeric and other keys, iscoupled to bus 502 for communicating information and command selectionsto processor 504. Another type of user input device is cursor control516, such as a mouse, a trackball, or cursor direction keys forcommunicating direction information and command selections to processor504 and for controlling cursor movement on display 512. This inputdevice typically has two degrees of freedom in two axes, a first axis(e.g., x) and a second axis (e.g., y), that allows the device to specifypositions in a plane.

Computer system 500 may implement the techniques described herein usingcustomized hard-wired logic, one or more ASICs or FPGAs, firmware and/orprogram logic which in combination with the computer system causes orprograms computer system 500 to be a special-purpose machine. Accordingto one embodiment, the techniques herein are performed by computersystem 500 in response to processor 504 executing one or more sequencesof one or more instructions contained in main memory 506. Suchinstructions may be read into main memory 506 from another storagemedium, such as storage device 510. Execution of the sequences ofinstructions contained in main memory 506 causes processor 504 toperform the process steps described herein. In alternative embodiments,hard-wired circuitry may be used in place of or in combination withsoftware instructions.

The term “storage media” as used herein refers to any media that storedata and/or instructions that cause a machine to operation in a specificfashion. Such storage media may comprise non-volatile media and/orvolatile media. Non-volatile media includes, for example, optical ormagnetic disks, such as storage device 510. Volatile media includesdynamic memory, such as main memory 506. Common forms of storage mediainclude, for example, a floppy disk, a flexible disk, hard disk, solidstate drive, magnetic tape, or any other magnetic data storage medium, aCD-ROM, any other optical data storage medium, any physical medium withpatterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, NVRAM, anyother memory chip or cartridge.

Storage media is distinct from but may be used in conjunction withtransmission media. Transmission media participates in transferringinformation between storage media. For example, transmission mediaincludes coaxial cables, copper wire and fiber optics, including thewires that comprise bus 502. Transmission media can also take the formof acoustic or light waves, such as those generated during radio-waveand infra-red data communications.

Various forms of media may be involved in carrying one or more sequencesof one or more instructions to processor 504 for execution. For example,the instructions may initially be carried on a magnetic disk or solidstate drive of a remote computer. The remote computer can load theinstructions into its dynamic memory and send the instructions over atelephone line using a modem. A modem local to computer system 500 canreceive the data on the telephone line and use an infra-red transmitterto convert the data to an infra-red signal. An infra-red detector canreceive the data carried in the infra-red signal and appropriatecircuitry can place the data on bus 502. Bus 502 carries the data tomain memory 506, from which processor 504 retrieves and executes theinstructions. The instructions received by main memory 506 mayoptionally be stored on storage device 510 either before or afterexecution by processor 504.

Computer system 500 also includes a communication interface 518 coupledto bus 502. Communication interface 518 provides a two-way datacommunication coupling to a network link 520 that is connected to alocal network 522. For example, communication interface 518 may be anintegrated services digital network (ISDN) card, cable modem, satellitemodem, or a modem to provide a data communication connection to acorresponding type of telephone line. As another example, communicationinterface 518 may be a local area network (LAN) card to provide a datacommunication connection to a compatible LAN. Wireless links may also beimplemented. In any such implementation, communication interface 518sends and receives electrical, electromagnetic or optical signals thatcarry digital data streams representing various types of information.

Network link 520 typically provides data communication through one ormore networks to other data devices. For example, network link 520 mayprovide a connection through local network 522 to a host computer 524 orto data equipment operated by an Internet Service Provider (ISP) 526.ISP 526 in turn provides data communication services through the worldwide packet data communication network now commonly referred to as the“Internet” 528. Local network 522 and Internet 528 both use electrical,electromagnetic or optical signals that carry digital data streams. Thesignals through the various networks and the signals on network link 520and through communication interface 518, which carry the digital data toand from computer system 500, are example forms of transmission media.

Computer system 500 can send messages and receive data, includingprogram code, through the network(s), network link 520 and communicationinterface 518. In the Internet example, a server 530 might transmit arequested code for an application program through Internet 528, ISP 526,local network 522 and communication interface 518. The received code maybe executed by processor 504 as it is received, and/or stored in storagedevice 510, or other non-volatile storage for later execution.

FIG. 6A illustrates a simplified configuration for local dimming withlight conversion. FIG. 6B illustrates a simplified configuration forlocal dimming with light conversion with compensation for spatial colornon-uniformity.

In one or more embodiments of the present invention, techniques for QDlocal dimming mitigates a variance in color point spread function (PSF)across the screen. This can be done mathematically accurately bycreating multiple light field simulations to change the parameters on anLCD solving matrix. A typical implementation can use nine light fieldsimulations; however, for consumer applications, a perfect mathematicalsolution is generally not needed.

As a particular embodiment of the present invention, logic 608determines one or more drive signals controlling backlight illuminationsources. Based on these drive signals backlight illumination sources(e.g., LEDs, LED 210) emit first light (e.g., broad spectrum whitelight, blue light, ultraviolet light) onto one or more light conversionlayers (e.g., quantum dot layers, QD sheet 212, or the like).

Based on the teachings herein, a backlight algorithm for light fieldsimulation 610, where the PSF is assumed to result in a uniform whitelight, defines a first path 612 for intermediate LCD drive values. Anadditional path corrects for variations from a white, uniform solutionto reduce spatial color non-uniformity.

As a further example, instead of corrections to the matrix, compensationlogic 614 can spatially scale the red, green, and blue primaries, in thecase of an RGB system. Alternatively to scaling, compensation logic 614can be accomplished by a suitable lookup table (LUT), e.g., a onedimensional, two dimensional, or three dimensional LUT. Compensation canbe determined for one or more color components.

EQUIVALENTS, EXTENSIONS, ALTERNATIVES AND MISCELLANEOUS

In the foregoing specification, possible embodiments of the inventionhave been described with reference to numerous specific details that mayvary from implementation to implementation. Thus, the sole and exclusiveindicator of what is the invention, and is intended by the applicants tobe the invention, is the set of claims that issue from this application,in the specific form in which such claims issue, including anysubsequent correction. Hence, no limitation, element, property, feature,advantage or attribute that is not expressly recited in a claim shouldlimit the scope of such claim in any way. The specification and drawingsare, accordingly, to be regarded in an illustrative rather than arestrictive sense. Numerous modifications and variations of theinvention are possible in light of the above teachings. Any definitionsexpressly set forth herein for terms contained in such claims shallgovern the meaning of such terms as used in the claims. It should befurther understood, for clarity, that exempli gratia (e.g.) means “forthe sake of example” (not exhaustive), which differs from id est (i.e.)or “that is.”

What is claimed is:
 1. An apparatus comprising: logic controlling one ormore illumination sources of a backlight configured to emit first lightonto one or more light conversion layers, the one or more lightconversion layers configured to be stimulated by the first light and toconvert at least a portion of the first light into second light; logicto control one or more light modulators, the one or more lightmodulators configured to modulate light transmitting through individualelements; logic to perform at least one light field simulation for abacklight point spread function to determine intermediate drive valuesfor the one or more light modulators; logic to determine a compensationlight field to adjust the intermediate drive values for the one or morelight modulators to mitigate spatial non-uniformity of the second light.2. The apparatus of claim 1 further comprising logic to adjust theintermediate drive values, the logic to adjust the intermediate drivevalues comprising at least one of a scaler and lookup table.
 3. Theapparatus of claim 1 wherein the second light is a broad spectrum light.4. The apparatus of claim 1 wherein the second light comprises of acombination of frequencies in red, blue and green portions of a visiblespectrum.
 5. A method for driving a local-dimming display comprising:emitting first light by one or more individually controllableillumination sources onto a quantum dot layer, the first light includingat least one of UV spectral components or blue light spectralcomponents; converting the first light into second light by the quantumdot layer; determining intermediate liquid crystal display modulationdrive signals by one or more light field simulations; determining acompensation field for spatial color non-uniformity related to travelingdistances of light from one or more illumination sources; andcompensating for the spatial color non-uniformity by adjusting theintermediate liquid crystal display modulation drive signals.
 6. Themethod claim 5 wherein the traveling distances account for one or morereflections.
 7. An apparatus comprising a processor and configured toperform the method recited in claim 5.